Genes and other biological markers are rapidly being identified that can provide presymptomatic estimates of risk to individuals for the eventual development of complex late-onset diseases. There is widespread public interest in obtaining risk information, particularly as treatments are developed to slow or prevent the onset of degenerative diseases. Many of the recently discovered gene markers are not deterministic genes, but rather susceptibility genes that interact with other, yet unidentified genes, and with factors such as age, gender, race, family history and environmental exposures. Therefore, genotyping individuals for susceptibility genes will require different protocols for providing risk assessment and counseling than those that have been used with deterministic genes. With few restrictions on the marketing and utilization of such tests, their usage may soon increase. Yet, there are almost no data available to understand who (e.g., age, sex, race) would seek susceptibility risk information once it is available; and why they would do so (e.g., to alleviate anxiety, to prepare financially). Nor is there information on the benefits or negative consequences of providing susceptibility risk information that could guide rational clinical decisions or public policy. This research project proposes to determine who actually chooses to obtain susceptibility genotyping for Alzheimer's disease (AD) and what the consequences of that information will be. Subjects will be randomized to one of two arms of the study. In the Control arm, risk will be estimated based upon family history. In the Intervention arm, risk will be estimated by family history and by genotyping ApoE - a common susceptibility polymorphism. Three clinical centers of care (Atlanta, New York City, and Cleveland) will enroll adult offspring of persons with AD; and using a carefully monitored protocol of counseling, assess the benefits and risks of providing this information. Determination of ApoE status will be used in a format that parallels likely clinical usage and will permit the development of guidelines for clinicians for genetic testing, risk assessment and appropriate counseling scenarios. ApoE determination and counseling, because of its inherent uncertainties, is an ideal model to develop new guidelines for whether and how best to use susceptibility gene markers in this and other diseases where such markers are or will be available in the near future.